The subject matter of this application is directed to mixed-signal converters of the sigma-delta (ΣΔ) noise shaping type, and more particularly, to mixed-signal digital-to-analog converters (DACs) that employ uniformly weighted elements.
Multi-bit sigma-delta DACs are widely used to reconstruct high precision analog signals in a stand-alone digital-to-analog conversion, or as a part of an analog-to-digital conversion circuit. The mismatch of the uniformly-weight analog elements, as a result of circuit imperfections, in this type of DAC introduces harmonic distortions that severely degrade the performance of the converter. Dynamic element matching (DEM) techniques have been used to improve the converter signal-to-noise ratio by either spectrally flattening out, or better yet, converting the harmonic distortions into a high-passed noise, which is beyond the signal bandwidth. As a result, the signal-to-noise ratio (SNR) and total-harmonic-distortion (THD) of the converter are greatly improved.
However, existing digital-to-analog conversion methods still suffer from 2nd-order DEMs not being able to shape higher order noise, requiring higher over-sampling ratios (OSR), and not being able to effectively handle low level signals. In addition, existing 2nd-order DEM logic take up large amount of space and do not work with three-level unit elements.
Accordingly, the inventors have identified a need in the art to increase the effectiveness of higher order DEMs which can achieve higher order noise shaping even at low signal levels, which are area-efficient, and which are able to operates with three-level unit elements.